Bellows-type valves have been utilized for heating systems fluid flow as seen in U.S. Pat. No. 1,875,672 in which the valve stem attached to an actuator is sealed by a bellows, the convolutions of which allow movement of a valve sealing disc on the stem into and out of contact with a valve seat. Other fluid control valves exemplified by U.S. Pat. No. 3,074,685 suggest use of a stepped valve stem and a helical spring urging the valve into a closed portion on a valve seat. Gas flow control valves sold by the Nupro Company of Willoughby, Ohio, under the model designations Nupro BK, HB and BN incorporate a sealing disc on a stepped stem in a bellows-type valve including a relatively long helically-coiled spring(s) above the valve housing. The Nupro HB and BN construction is believed to incorporate at least parts of the construction shown in U.S. Pat. No. 4,634,099, assigned to the Nupro Company. These valves also incorporate a valve actuator piston attached to the top of the valve stem which piston is operable to open and shut the valve at a valve seat below an externally pressurized bellows surrounding the opposite end of the valve stem. Similar valves are sold by Parker Hannifin Corp. of Cleveland, Ohio under the Parker P4K designation and by Fujikin International, Inc. of Osaka, Japan under the FUJIKIN FP designation. Each of the above gas flow control valves includes an inclined flow passage extending outwardly from below the valve seat and an overall relatively high profile due to the inclusion of a coil spring biasing of the actuator piston The '099 patent does suggest an alternative for biasing the valve alternatively in an open condition but since different springs are utilized the valve is not symmetrical. Further, these valve apparently are not capable of double-acting operation. Additionally, the above gas flow valves do not provide an accurate valve stem guide, particularly one which is inherently non-particulating and contaminant free. Still further they include a relatively large internal volume necessitating a high volume of gases to be removed from the valve during purging operations. Additionally these prior art gas valves have a relatively small seal and seat diameter resulting in a relatively low gas flow rate through the annular orifice between the seal and seat.